Printer ribbon cartridges for use with dot matrix and other types of impact computer printers are well known in the prior art. Many printer ribbon cartridges house an inked ribbon in the form of a continuous loop. In use, the ribbon is continuously withdrawn from one arm of the cartridge and returned to the opposite arm as a cartridge drive mechanism is rotated by a printer driver. Other printer ribbon cartridges transfer ribbon between a pair of reels as the printer operates. Printer ribbon cartridges are conventionally mounted in a printer so that an exposed length of ribbon between the arms of the cartridge passes between a printing surface and a print head. In the case of both line and character dot matrix computer printers, ink is transferred from the exposed length of the ribbon to the paper by the actuation of wires that form part of a print head. The ribbon is used until the ink on the ribbon is depleted and the print quality becomes unacceptable.
Acceptable print quality is determined by measuring the amount of ink deposited on a print media, e.g., paper. The light reflecting off a printed rectangle on the paper is used to measure the optical density of the print and is indicated in optical density units (O.D.U.). Using this technique, it is possible to determine when a ribbon has reached its minimum density level and is no longer producing acceptable print. The industry standard for minimum acceptable density is 0.50 O.D.U. Once the density approaches the minimum acceptable density, the printer cartridge or ribbon is usually replaced. Frequent replacement of the printer cartridge is costly and inconvenient. While the replacement of used ribbons with new ribbons is possible, this is time-consuming, messy, and requires disassembly of the printer cartridge. Thus, printer ribbon cartridges are usually disposed of, rather than recycled, even though the ribbon is still strong enough to be reused. In the past, cartridge life has been extended by re-inking the ribbon of a cartridge, without removal of the ribbon. Re-inking the ribbon allows the cartridge to continue producing acceptable print for a longer period of time. Thus, the cost and burden normally associated with replacing the cartridge or ribbon is greatly reduced.
Both internal and external re-inking mechanisms for re-inking ribbon are known in the prior art. An internal re-inking device normally comprises an ink supply combined with a mechanism for transferring the ink from the ink supply to the ribbon. In this regard, the mechanism normally comprises an absorbent element such as a foam ring or a wick that stores ink and a transfer roller that transfers the ink to the ribbon. If a foam ring is used, the ink supply is limited to the amount of ink the foam ring is capable of absorbing. When the ink supply is depleted, the foam ring is replaced or manually supplied with additional ink, which may require disassembly of the printer cartridge. A wick, on the other hand, absorbs ink from an internal source. However, as the ink supply diminishes, the wick tends to dry out. If the wick dries out before the ink supply is depleted, the remaining ink is wasted.
When an external re-inking device is used to re-ink the ribbon, the printer cartridge is usually removed from the computer printer and attached to the external re-inking device so that the ribbon is partially removed from the cartridge and threaded through the external re-inking device. The ink is applied to the ribbon either directly as it passes through an external ink supply or via a pump that applies ink to a transfer mechanism. In either case, an absorbent element such as a foam ring or wick is not utilized.
While the foregoing mechanisms have greatly contributed to extending the useful life of printer ribbon cartridges, they are not entirely satisfactory. Specifically, there exists a need for a printer ribbon cartridge comprising an internal re-inking mechanism that extends ribbon life, decreases cost and ink waste, and eliminates the need for disassembly, removal or manually replenishing the ink supply. The present invention is directed to providing such a printer ribbon cartridge.